1. Field of the Invention
The present invention relates to a power converter control circuit, and particularly, a power converter control circuit with reduced pins.
2. Description of the Related Art
Recently, the fast development of the liquid-crystal display (LCD) has enabled the light-emitting diode (LED) backlight to gradually replace the traditional cold-cathode fluorescent lamps (CCFL) backlight.
Refer to FIG. 1, FIG. 1 shows the prior art of a light-emitting diode driving circuit with the boost-up function, comprising a boost-up circuit 10, a voltage division circuit 30, an integrated control circuit 40, a light-emitting diode 20, and a feedback resistor RFB.
As a power transistor T1 is turned on, an input voltage Vin is bridged over a power saving device L1, such that a current on a power saving device L1 is increasing linearly with time and electrical energy is storing in the power saving device L1. As the preset turn-on time is reached, the power transistor T1 is shut down immediately, such that the electrical power saved in the power saving device L1 is transmitted to the output of the boost-up circuit 10 through a diode D1 and charged a capacitor C2. The above procedures are repeated iteratively to boost up the input voltage Vin to the preset threshold voltage level of the boost-up circuit 10. This is the principle of boosting voltage.
Furthermore, an output end of the boost-up circuit 10 is electrically connected in series to the light-emitting diode and the feedback resistor RFB, wherein a non-grounded end of the feedback resistor RFB is electrically connected to the feedback signal pin FB of the control circuit 40. A feedback voltage of the feedback circuit is transmitted to the control circuit 40 and enables the control circuit 40 to transmit a control signal to a gate of the power transmitter T1, such that a setup current can be generated.
Furthermore, the over-voltage protection method is by transmitting the output voltage of the boost-up circuit 10 through the voltage division circuit 30 to output a voltage division to the over-voltage signal pin OVP, then the voltage division is compared with a reference voltage of a over-voltage comparator (not shown) within the control circuit 40.
Besides, the current detection method is to enable a source of the power transistor T1 to send a signal to the current detection signal pin CS via the over-current detection resistor RCS.